Description: Seawater-derived neodymium (Nd) isotope ratios of sediment coatings have increasingly been used in paleoceanographic reconstructions to derive information on the past variability of deepwater sources and mixing. Dissolved Nd in seawater originates from weathering processes of the continental crust. It is delivered to the oceans either through boundary exchange processes or in dissolved or particulate form through riverine input (Frank, 2002). The use of radiogenic Nd isotopes as oceanic tracers is enabled by the average ocean residence time of Nd, which is similar to the global mixing time of oceans (ca 400 – 2,000 years) and by their independence of stable isotope fractionation by biological or physical processes (van de Flierdt et al., 2006). In this study, we investigate Nd isotope ratios of both core-top and Holocene sediment samples (leachates and detritus) and compare them to modern seawater Nd isotope signatures in the eastern Fram Strait, as well as to a multitude of proxy indicators for the climatic and oceanographic variability in the eastern Fram Strait during the past 8,500 years. The West Spitsbergen Current (WSC) represents the major means of northward heat transport to the Arctic Ocean via eastern Fram Strait. While the upper layers of the WSC are fed by warm and saline Atlantic Water derived from the North Atlantic Current, deepwater inflow through eastern Fram Strait is still subject of debate. Our study is primarily intended to reconstruct Holocene variability of bottom water sources in the Arctic Gateway. However, relatively radiogenic Nd isotope ratios of the leached fraction since the late Holocene suggest a contribution of fine lithic grains transported by sediment-laden sea ice from the East Siberian shelves to the Fram Strait (Dethleff and Kuhlmann, 2009). This is in contrast to the less radiogenic Nd isotope ratios of present-day intermediate and deep water in the area documenting an Atlantic source. We therefore suggest an alternative explanation, which is input and transport of sediment material with preformed sediment coatings from source areas on the Siberian shelf to the Central Arctic and the eastern Fram Strait. The eastern Fram Strait has been the bottleneck of Arctic sea ice export and main ablation area for ice-transported (fine-grained) material since approximately 5 cal ka BP. References Dethleff, D. and Kuhlmann, G., 2009. Entrainment and export of fine-grained surface deposits into new ice in the southwestern Kara Sea, Siberian Arctic. Continental Shelf Research, 29, 691-701. Frank, M., 2002. Radiogenic Isotopes: Tracers of Past Ocean Circulation and Erosional Input. Reviews of Geophysics, 40, 1001, 10.1029/2000RG000094. Van de Flierdt, T., Robinson, L.F., Adkins, J.F. and Hemming, S.R., 2006. Temporal stability of the neodymium isotope signature of the Holocene to glacial North Atlantic. Paleoceanography, 21, PA4102

Description: The rare earth elements (REEs) with their systematically varying properties are powerful tracers of continental inputs, particle scavenging intensity and the oxidation state of seawater. However, their generally low (∼pmol/kg) concentrations in seawater and fractionation potential during chemical treatment makes them difficult to measure. Here we report a technique using an automated preconcentration system, which efficiently separates seawater matrix elements and elutes the preconcentrated sample directly into the spray chamber of an ICP-MS instrument. The commercially available “seaFAST” system (Elemental Scientific Inc.) makes use of a resin with ethylenediaminetriacetic acid and iminodiacetic acid functional groups to preconcentrate REEs and other metals while anions and alkali and alkaline earth cations are washed out. Repeated measurements of seawater from 2000 m water depth in the Southern Ocean allows the external precision (2σ) of the technique to be estimated at 〈23% for all REEs and 〈15% for most. Comparison of Nd concentrations with isotope dilution measurements for 69 samples demonstrates that the two techniques generally agree within 15%. Accuracy was found to be good for all REEs by using a five point standard addition analysis of one sample and comparing measurements of mine water reference materials diluted with a NaCl matrix with recommended values in the literature. This makes the online preconcentration ICP-MS technique advantageous for the minimal sample preparation required and the relatively small sample volume consumed (7 mL) thus enabling large data sets for the REEs in seawater to be rapidly acquired.